Contribution of time-related environmental tracing combined with tracer tests for characterization of a groundwater conceptual model: a case study at the Séchilienne landslide, western Alps (France)

Abstract

Groundwater-level rise plays an important role in the activation or reactivation of deep-seated landslides and so hydromechanical studies require a good knowledge of groundwater flows. Anisotropic and heterogeneous media combined with landslide deformation make classical hydrogeological investigations difficult. Hydrogeological investigations have recently focused on indirect hydrochemistry methods. This study aims at determining the groundwater conceptual model of the Séchilienne landslide and its hosting massif in the western Alps (France). The hydrogeological investigation is streamlined by combining three approaches: a one-time multitracer test survey during high-flow periods, a seasonal monitoring of the water stable-isotope content and electrical conductivity, and a hydrochemical survey during low-flow periods. The complexity of the hydrogeological setting of the Séchilienne massif leads to development of an original method to estimate the elevations of the spring recharge areas, based on topographical analyses and water stableisotope contents of springs and precipitation. This study shows that the massif supporting the Séchilienne landslide is characterized by a dual-permeability behaviour typical of fractured-rock aquifers where conductive fractures play a major role in the drainage. There is a permeability contrast between the unstable zone and the intact rock mass supporting the landslide. This contrast leads to the definition of a shallow perched aquifer in the unstable zone and a deep aquifer in the intact massif hosting the landslide. The perched aquifer in the landslide is temporary, mainly discontinuous, and its extent and connectivity fluctuate according to the seasonal recharge.

Functioning and precipitation-displacement modelling of rainfall-induced deep-seated landslides subject to creep deformation

“…Heterogeneous, anisotropic and discontinuous properties of the landslide lead to a discontinuous perched fractured reservoir. The massif supporting the Séchilienne landslide is characterised by a dual-permeability behaviour typical of fractured rock aquifers where conductive fractures play a major role in the drainage (Vallet et al 2015b). In addition, the sedimentary deposits distributed above the landslide (Fig.…”

“…The perched aquifer in the landslide is temporary, mainly discontinuous, and its extent and connectivity fluctuate according to short-term recharge variations (Vallet et al 2015b). The recharge of the landslide-perched aquifer is essentially local, enhanced by the trenches and the counterscarps which tend to limit the runoff and to facilitate groundwater infiltration in the landslide area.…”

“…The recharge of the landslide-perched aquifer is essentially local, enhanced by the trenches and the counterscarps which tend to limit the runoff and to facilitate groundwater infiltration in the landslide area. However, during high-flow periods, the recharge area of the landslide-perched aquifer may become larger than the landslide surface and may include the remote sedimentary cover-perched aquifer (Guglielmi et al 2002;Vallet et al 2015b).…”

“…The recharge areas of the deep aquifer (identical to that of the soil reservoir) and of the perched aquifer are estimated to 3 km 2 and 0.05 km 2 , respectively (Fig. 2), according to Guglielmi et al (2002) and Vallet et al (2015b). The recharge area of the perched aquifer is limited to the high motion zone of the landslide.…”

Evidencias hidrogeoquímicas e isotópicas sobre el origen del agua subterránea en la cuenca hidrográfica Río Actopan, Estado de Veracruz

“…Si se integra el concepto de conductividad hidráulica y el agua como agente geológico (Toth, 1999) se pueden generar modelos conceptuales detallados de flujo de agua subterránea a escala de cuenca (Mádl-Szönyi and Toth, 2015). Sin embargo, la conceptualización de sistemas acuíferos anisotrópicos y heterogéneos plantean un reto importante respecto a las investigaciones hidrológicas clásicas (Vallet et al, 2015).…”